Electrochemical oxidation of mono- and disaccharides at fresh as well as oxidized copper electrodes in alkaline media

The electrochemical oxidation of mono- and disaccharides in a sodium hydroxide solution at a fresh as well as on an oxidized Cu rotating disk electrode (RDE) is reported. It is demonstrated herein that the oxidation of disaccharides is not similar to that of monosaccharides as exemplified by a comparative electrooxidation study of glucose and maltose as typical mono- and disaccharides, respectively. The oxidation of monosaccharides (glucose, galactose, mannose) at a fresh Cu RDE gave approximately 12 electrons (n), and that of disaccharides (cellobiose, isomaltose, laminaribiose, mannobiose, maltose) gave n ranging between 3 and 13. The electrooxidation of disaccharides was also studied as a function of sodium hydroxide concentration as well as applied potential, but these parameters were not found to affect the number of electrons transferred or the heterogeneous rate constants to a significant degree. Further investigations of the electrooxidation of glucose and maltose at an oxidized Cu RDE showed that, for maltose, the number of electrons transferred and the heterogeneous electrooxidation rate constant (k) were dependent on the oxidative treatment time. This dependence was not associated with an increased surface roughness of the electrode as the n value for glucose was not affected by the oxidative treatment time. Up to n = 19 could be observed for maltose and the kinetic constant reached 5 x 10(-3) cm s(-1) compared to that for a freshly cleaned electrode (5 x 10(-4) cm s(-1)). (C) 1999 Elsevier Science S.A. All rights reserved.